The present invention relates to a heating cylinder device for melting resin material in a molding machine such as an injection molding machine or an extruder or the like which performs mold forming using such resin as a material, and in particular to such a heating cylinder device which can more effectively accomplish steady and uniform heating up of such resin material.
In the prior art with regard to this sort of heating cylinder device for a molding machine, demands are nowadays constantly being made for shortening of the injection cycle, in order to improve productivity. Further, it is also very desirable to reduce the power consumption of the heating means for the resin, which typically accounts for about a third of the total power consumption of the injection molding machine. Reduction of the power required for setting up the machine and bringing its various parts to appropriate operating temperatures is effective for meeting this end. And yet further it is a constant requirement to improve the precision of the molded products made by the molding machine, which entails as accurate control of heating of the resin material as possible. Accordingly, proper heat management of the heating cylinder device for the resin is crucial for meeting these needs.
Now, in the prior art, such a heating cylinder device typically has had a plurality of heating zones arranged, and has basically been shaped as a uniform hollow cylinder, with a plurality of annular band shaped heaters arranged longitudinally around its outer surface along the lengthwise direction, each such heater being wrapped around one of the heating zones. These heaters are energized in such appropriate amounts as to keep the successive heating zones at appropriate temperatures to ensure proper heating up of the resin material to be molded, as such resin material is progressively moved down along the central hole of the hollow heating cylinder device by the action of a plunger or the like. Thus, the heat management for these heating zones is performed.
However, the problems with such a prior art type of heating cylinder device are as follows.
First, because the thickness of the heating cylinder has been uniform for each of the heating zones, thermal interferences tend to develop between neighboring ones of the heating zones, in addition to the interferences arising from external sources such as changes in the ambient temperature, fluctuations in the system due to the motion of the resin material which is being heated up, changes in the temperature of the resin material, dissipation of heat in injecting the resin material, and so on. Accordingly accurate temperature control of the resin becomes very difficult. Further, because the thickness of the heating cylinder has been uniform for each of the heating zones, each of these heating zones has approximately the same heat capacity, and in view of the different temperatures up to which these zones are required to be heated this causes difficulties in heating control.
Secondly, because each heating zone as defined along the axis of the heating cylinder device is contiguous to the next, and the heating cylinder device is constructed basically as a uniform hollow cylinder, the abovementioned thermal interferences which tend to develop between neighboring ones of the heating zones are very strong, and present a substantial obstacle to the proper heat control of the various heating zones.
Thirdly, because the thickness of the walls of the heating cylinder device, in other words the distance between its outer circumferential surface on which, in the above outlined prior art, the band shaped heaters are mounted, and its inner hole in which the resin is flowing, is very substantial, a time delay occurs in the transfer of heat from the heaters to the resin, and accordingly precise temperature control of the resin becomes very difficult, and fluctuations in the system, such as alterations in the ambient temperature, changes in the flow speed of the resin and in the temperature at which said resin is supplied to the heating cylinder device, and changes in the dissipation of heat that occurs when injecting the resin, cause great problems with regard to temperature control, because of the lack of responsiveness of the system.
Fourthly and lastly, because the thermal capacity of each of the heating zones is approximately the same, and because the resistance to heat flow from each of the heating zones to the outside is approximately the same, this further causes thermal interferences between the neighboring heating zones to occur.